Field of the Invention
The present disclosure relates to an image forming apparatus provided with an optical scanning device having a transparent window for passing a laser beam and a shutter for covering the transparent window for passing the laser beam.
Description of the Related Art
An electro-photographic image forming apparatus, such as a laser beam printer, a digital copying machine and the like, is provided with an optical scanning device for exposing a photosensitive body. The optical scanning device scans a surface of the photosensitive body with a light beam emitted from a semiconductor laser by deflecting the light beam with a rotary polygon mirror. With such an operation, an electrostatic latent image is formed on the surface of the photosensitive body. This electrostatic latent image is developed by adhering toner thereto, so that an image is formed on the recording sheet by transferring the toner image.
In recent years, with popularization of color image forming apparatuses, a so-called tandem system in which a dedicated photosensitive body for each color is provided and an image of each color is formed on an intermediate transfer body at the same time has been considered as the mainstream of the color image forming apparatuses. In the tandem system color image forming apparatus, a so-called four-in-one type optical scanning device in which exposure processing of four colors is executed by a single rotary polygon mirror has been widely used because of its favorable unit size and cost.
Further, from among various four-in-one type optical scanning devices, a so-called lower surface exposure system in which the optical scanning device exposes photosensitive bodies from a side of lower surfaces of the photosensitive bodies has been generally used in order to efficiently use and conserve an internal space of the image forming apparatus. In a case where a process cartridge integrally configured of a photosensitive body and a development unit is detached from or attached to the image forming apparatus provided with the lower surface exposure system optical scanning device in order to execute maintenance and inspection work, toner may be scattered from the process cartridge because of the impact arising from detachment or attachment of the process cartridge. If such scattered objects fall on and adhere to a light emitting window of the optical scanning device, scanning light travelling toward the photosensitive body may be interrupted by the scattered objects and a stripe-like image defect may occur. Therefore, in order to prevent the scattered objects from adhering to the optical scanning device, an opening-closing type dustproof shutter is commonly disposed on an upper portion of the lower surface exposure type optical scanning device. In particular, a flat-plate sliding shutter is commonly used because a space between the photosensitive body and the optical scanning device has limitation. Japanese Patent Application Laid-Open No. 2007-148276 discusses a mechanism for pressing a pair of lever members to open and close a dustproof shutter by using a driving motor and an eccentric cam.
However, with the mechanism for opening and closing the dustproof shutter by using power of the driving motor as discussed in Japanese Patent Application Laid-Open No. 2007-148276, the image forming apparatus is increased in size while the configuration thereof is complicated because a driving motor and a wire harness are disposed thereon. Further, in the above-described shutter, an opening-closing position of the shutter has to be managed properly. If the opening-closing position thereof is not managed properly, the shutter may interrupt the optical path of the light beam if the shutter is not pushed sufficiently, or the shutter may be damaged by being pushed excessively. In order to solve the above problem, for example, it is necessary to provide a sensor, such as a photo-interrupter, for detecting a terminal position of the shutter, or to dispose a rotation movement mechanism, such as lever members with high precision.
In view of the above mentioned conditions, the present invention is directed to a simple mechanism capable of reliably operating a shutter while ensuring an opening-closing position of the shutter.